1. Technical Field
The present invention relates to an optical multilayer filter, a method for manufacturing the same, and an electronic apparatus in which the optical multilayer filter is built.
2. Related Art
In general, optical multilayer filters, such as antireflection films, half mirrors, and low-pass filters, frequently used in electronic apparatuses are composed of a substrate and an inorganic thin film formed on the substrate by vacuum deposition, for example. The inorganic thin film typically has a multilayered structure in which a high refractive index film made of titanium oxide (TiO2), and a low refractive index film made of silicon oxide (SiO2), are alternately deposited, for example.
The inorganic thin film, however, is easily charged with static electricity since it has no conductivity, which is derived from the structure. Therefore, dust easily sticks on the surface of the optical multilayer filter, which may adversely affect optical characteristics of electronic apparatuses in which the filter is built.
As a countermeasure against static electricity of such a non-conductive transparent substrate, an example is disclosed in claims of JP-A-2004-233501 in which a transparent conductive film is provided on an outer surface of dust-proof glass. Such transparent conductive film can maintain transparency of glass and effectively remove static electricity since it has conductivity.
However, if the transparent conductive film cited in JP-A-2004-233501 is provided on the uppermost surface layer of an optical multilayer filter, the whole optical characteristic of the optical multilayer filter may be changed since the optical characteristic of the film serving as the uppermost surface layer is important in the optical multilayer filter. In addition, providing the transparent conductive film by another process separated from a process manufacturing the optical multilayer filter has a disadvantage in costs.